Erythrocyte cation transport activities as a function of cell age

Differential Responses of Young and Old Erythrocytes Stored with Vitamin C and Vitamin E in AS-7

Oxidative stress causes biochemical and morphological alterations in erythrocytes. The primary factors contributing to oxidative stress are aging and storage. Antioxidants significantly alleviate oxidative stress. Therefore, this study aimed to investigate the response of young and old erythrocytes to Vitamin C and Vitamin E during storage. Erythrocytes were separated into young and old by the Percoll method. Each erythrocyte subpopulation was categorized into i) Control [Additive Solution-7 (AS-7)] and ii) VC+VE group [Vitamin C and Vitamin E in AS-7] and stored for 21 days at 4˚C. Oxidative stress, antioxidant, and aging markers were analyzed on days 1, 14, and 21. The activity of antioxidant enzymes was similar throughout storage in Young cells. However, superoxide dismutase activity elevated in Old cells (Control and VC+VE) on days 1 and 21. Catalase activity increased on days 14 and 21, while glutathione peroxidase increased on days 1 and 14 in Old Controls. However, in Old VC+VE, catalase increased on day 21 and glutathione peroxidase increased on day 1. Advanced oxidation protein products, superoxides, glutathione, and uric acid increased in old cells throughout the storage. Malondialdehyde decreased in Old VC+VE compared to Old Control on days 14 and 21 respectively. Sialic acids and glutamate oxaloacetate transaminase activity were higher in young cells compared to old cells. Young cells exhibited lower oxidative changes throughout storage. Vitamin C and Vitamin E were effective in maintaining the redox balance in old cells. These findings emphasize the need for specific approaches for different subpopulations during erythrocyte banking.

How Do Red Blood Cells Die?

Normal human red blood cells have an average life span of about 120 days in the circulation after which they are engulfed by macrophages. This is an extremely efficient process as macrophages phagocytose about 5 million erythrocytes every second without any significant release of hemoglobin in the circulation. Despite large number of investigations, the precise molecular mechanism by which macrophages recognize senescent red blood cells for clearance remains elusive. Red cells undergo several physicochemical changes as they age in the circulation. Several of these changes have been proposed as a recognition tag for macrophages. Most prevalent hypotheses for red cell clearance mechanism(s) are expression of neoantigens on red cell surface, exposure phosphatidylserine and decreased deformability. While there is some correlation between these changes with aging their causal role for red cell clearance has not been established. Despite plethora of investigations, we still have incomplete understanding of the molecular details of red cell clearance. In this review, we have reviewed the recent data on clearance of senescent red cells. We anticipate recent progresses in in vivo red cell labeling and the explosion of modern proteomic techniques will, in near future, facilitate our understanding of red cell senescence and their destruction.

Apoptotic death in erythrocytes of lamprey Lampetra fluviatilis induced by ionomycin and tert-butyl hydroperoxide

The work examined the effects of Ca²⁺ overload and oxidative damage on erythrocytes of river lamprey Lampetra fluvialtilis. The cells were incubated for 3h with 0.1-5μM Ca²⁺ ionophore ionomycin in combination with 2.5mM Ca²⁺ and 10-100μM pro-oxidant agent tert-butyl hydroperoxide (tBHP). The sensitivity of lamprey RBCs to studied compounds was evaluated by the kinetics of their death. Both toxicants induced dose- and time dependent phosphatidylserine (PS) externalization (annexin V-FITC labeling) and loss of membrane integrity (propidium iodide uptake). Highest doses of ionomycin (1-2μM) increased the number of PS-exposed erythrocytes to 7-9% within 3h, while 100μM tBHP produced up to 50% of annexin V-FITC-positive cells. Caspase inhibitor Boc-D-FMK (50μM), calpain inhibitor PD150606 (10μM) and broad protease inhibitor leupeptin (200μM) did not prevent ionomycin-induced PS externalization, whereas tBHP-triggered apoptosis was blunted by Boc-D-FMK. tBHP-dependent death of lamprey erythrocytes was accompanied by the decrease in relative cell size, loss of cell viability, activation of caspases 9 and 3/7, and loss of mitochondrial membrane potential, but all these processes were partially attenuated by Boc-D-FMK. None of examined death-associated events were observed in ionomycin-treated erythrocytes except activation of caspase-9. Incubation with ionomycin did not alter intracellular K⁺ and Na⁺ content, while exposure to tBHP resulted in 80% loss of K⁺ and 2.8-fold accumulation of Na⁺. Thus, lamprey erythrocytes appear to be more susceptible to oxidative damage. Ca²⁺ overload does not activate the cytosolic death pathways in these cells.

The influence of erythrocyte maturity on ion transport and membrane lipid composition in the rat

Significant relationships between ion transport and membrane lipid composition (cholesterol, total phospholipids and sphingomyelins) were found in erythrocytes of salt hypertensive Dahl rats. In these animals mean cellular hemoglobin content correlated negatively with Na(+)-K(+) pump activity and Na(+) leak but positively with Na(+)-K(+) cotransport activity. Immature erythrocytes exhibit lower mean cellular hemoglobin content (MCHC) than mature ones. The aim of the present study was to find a relationship between erythrocyte maturity, membrane lipid composition and ion transport activity in Wistar rats aged three months which were subjected to repeated hemorrhage (blood loss 2 ml/day for 6 days) to enrich circulating erythrocytes with immature forms. Immature and mature erythrocyte fractions in control and hemorrhaged rats were separated by repeated centrifugation. Hemorrhaged rats had increased number of reticulocytes but reduced hematocrit and MCHC compared to control rats. Immature erythrocytes of hemorrhaged rats differed from mature ones of control animals by elevated Na(+)-K(+) pump activity, reduced Na(+)-K(+) cotransport activity and increased Rb(+) leak. These ion transport changes in immature erythrocytes were accompanied by higher concentration of total phospholipids in their cell membranes. Membrane phospholipid content correlated positively with Na(+)-K(+) pump activity and cation leaks but negatively with Na(+)-K(+) cotransport activity. Moreover, they were also negatively related with MCHC which correlated negatively with Na(+)-K(+) pump activity and Rb(+) leak but positively with Na(+)-K(+) cotransport activity. Thus certain abnormalities of erythrocyte ion transport and membrane lipid composition detected in hypertensive animals might be caused by higher incidence of immature cells.

The pathophysiology and consequences of red blood cell storage

Red cell transfusion therapy is a common treatment modality in contemporary medical practice. Although blood collection and administration is safer and more efficient than ever before, red cells undergo multiple metabolic and structural changes during storage that may compromise their functionality and viability following transfusion. The clinical relevance of these changes is a hotly debated topic that continues to be a matter of intense investigation. In the current review, we begin with an in-depth overview of the pathophysiological mechanisms underlying red cell storage, with a focus on altered metabolism, oxidative stress and red cell membrane damage. We proceed to review the current state of evidence on the clinical relevance and consequences of the red cell storage lesion, while discussing the strengths and limitations of clinical studies.

Red blood cell subpopulations in freshly drawn blood: application of proteomics and metabolomics to a decades-long biological issue

BACKGROUND

It has long been known that red blood cells comprise various subpopulations, which can be separated through Percoll density gradients.

MATERIALS AND METHODS

In this study, we performed integrated flow cytometry, proteomic and metabolomic analyses on five distinct red blood cell subpopulations obtained by Percoll density gradient separation of freshly drawn leucocyte-depleted erythrocyte concentrates. The relation of density gradient fractions to cell age was confirmed through band 4.1a/4.1b assays.

RESULTS

We observed a decrease in size and increase in cell rugosity in older (denser) populations. Metabolomic analysis of fraction 5 (the oldest population) showed a decrease of glycolytic metabolism and of anti-oxidant defence-related mechanisms, resulting in decreased activation of the pentose phosphate pathway, less accumulation of NADPH and reduced glutathione and increased levels of oxidized glutathione. These observations strengthen conclusions about the role of oxidative stress in erythrocyte ageing in vivo, in analogy with results of recent in vitro studies. On the other hand, no substantial proteomic differences were observed among fractions. This result was partly explained by intrinsic technical limitations of the two-dimensional gel electrophoresis approach and the probable clearance from the bloodstream of erythrocytes with membrane protein alterations. Since this clearance effect is not present in vitro (in blood bank conditions), proteomic studies have shown substantial membrane lesions in ageing red blood cells in vitro.

CONCLUSION

This analysis shows that the three main red blood cell subpopulations, accounting for over 92% of the total RBC, are rather homogeneous soon after withdrawal. Major age-related alterations in vivo probably affect enzyme activities through post-translational mechanisms rather than through changes in the overall proteomic profile of RBC.

Correction factors for estimating potassium concentrations in samples with in vitro hemolysis: a detriment to patient safety

CONTEXT

Correction factors have been proposed for estimating true potassium concentrations in blood samples with evidence of in vitro hemolysis.

OBJECTIVE

We used 2 different models of true (ie, nonsimulated) in vitro hemolysis to evaluate the clinical utility of correction factors for estimating potassium concentrations in samples with evidence of in vitro hemolysis.

DESIGN

Potassium correction factors were derived using 2 different models. In model 1, potassium and plasma hemoglobin were measured with the Hitachi 747 analyzer in 132 paired blood samples, with each pair consisting of 1 sample with evidence of hemolysis and 1 without, collected during the same phlebotomy procedure. The change in measured potassium concentration was plotted versus the change in plasma hemoglobin concentration for each pair of samples. In model 2, the potassium levels of 142 784 blood samples and the corresponding hemolytic index values were measured with the Beckman LX20 analyzer. Potassium concentrations at the 10th, 25th, 50th, 75th, and 90th percentiles were calculated for each hemolysis index category.

RESULTS

From our 2 models, we derived correction factors expressing an increase in potassium concentration of 0.51 and 0.40 mEq/L for every increase in plasma hemoglobin concentration of 0.1 g/dL. These correction factors are much higher than those reported in studies that simulated in vitro hemolysis by freeze-thaw lysis or osmotic disruption of whole blood.

CONCLUSIONS

Use of correction factors for estimating the true potassium concentration in samples with evidence of in vitro hemolysis is not recommended. Derivation of correction factors by using samples with nonsimulated in vitro hemolysis suggests that the actual increase in potassium in hemolyzed samples is much higher than that reported in previous studies that produced hemolysis with artificial means.

Effects of darbepoetin injections on erythrocyte membrane transport protein expressions in humans

The present study investigated the effects of injected darbepoetin [novel erythropoietin stimulating protein (NESP)] on the density of three erythrocyte membrane transport proteins: the lactate-H+ cotransporter (monocarboxylate transporter 1), the chloride/bicarbonate exchanger 1 (anion exchanger 1), and the water channel aquaporin 1. Thirteen subjects were injected with NESP once a week for 4 wk. Blood samples were obtained before, during, and after the injection period, and the erythrocyte transport proteins were determined by Western blotting. The NESP injections induced a transient increase in hematocrit, red cell volume, and reticulocyte fraction. The density of aquaporin 1 protein was higher (maximal increase +59%) ( P < 0.01) during the injection period compared with the preinjection value and lower ( P < 0.01) after the injection period. The density of anion exchanger 1 protein was higher (maximal increase +15%) ( P < 0.05) during the injection period compared with the preinjection value and tended ( P = 0.06) to be lower after the injection period than before the injection period. The density of the erythrocyte monocarboxylate transporter 1 protein was higher (maximal increase +43%) ( P < 0.05) during the injection period than in the preinjection period. Age separation experiments using self-creating Percoll gradients demonstrated a higher density of membrane transport proteins in young red blood cells. These data suggest that the NESP-induced increase in membrane transport proteins is caused by a higher fraction of newly formed erythrocytes (and reticulocytes), which have a higher density of membrane transport proteins. However, increased incorporation of membrane proteins during erythrocyte formation may also be involved. We suggest that NESP improves the quality of erythrocyte membrane transport through these mechanisms.

Relationships between membrane lipids and ion transport in red blood cells of Dahl rats

Distinct changes of membrane lipid content could contribute to the abnormalities of ion transport that take part in the development of salt hypertension in Dahl rats. The relationships between lipid content and particular ion transport systems were studied in red blood cells (RBC) of Dahl rats kept on low- and high-salt diets for 5 weeks since weaning. Dahl salt-sensitive (SS/Jr) rats on high-salt diet had increased blood pressure, levels of plasma triacylglycerols and total plasma cholesterol compared to salt-resistant (SR/Jr) rats. Furthermore, RBC of SS/Jr rats differed from SR/Jr ones by increased content of total membrane phospholipids, but membrane cholesterol was not changed significantly. SS/Jr rats had higher RBC intracellular Na+ (Na(i)+) content and enhanced bumetanide-sensitive Rb+ uptake. RBC membrane content of cholesterol and phospholipids correlated positively with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and also with Rb+ leak. The content of phosphatidylserines plus phosphatidylinositols was positively associated with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and with Rb+ leak. The content of sphingomyelins was positively related to Na+-K+-2Cl- cotransport activity and negatively to ouabain-sensitive Rb+-K+ exchange. We can conclude that observed relationships between ion transport and the membrane content of cholesterol and/or sphingomyelins, which are known to regulate membrane fluidity, might participate in the pathogenesis of salt hypertension in Dahl rats.

Cell age-related monovalent cations content and density changes in stored human erythrocytes

Conversion of erythrocyte membrane protein 4.1b to 4.1a occurs through a non-enzymatic deamidation reaction in most mammalian erythrocytes, with an in vivo half-life of approximately 41 days, making the 4.1a/4.1b ratio a useful index of red cell age [Inaba and Maede, Biochim. Biophys. Acta 944 (1988) 256-264]. Normal human erythrocytes distribute into subpopulations of increasing cell density and cell age when centrifuged in polyarabinogalactan density gradients. We have observed that, when erythrocytes were stored at 4 degrees C under standard blood bank conditions, the deamidation was virtually undetectable, as cells maintained the 4.1a/4.1b ratio they displayed at the onset of storage. By measuring the 4.1a/4.1b values in subpopulations of cells of different density at various time points during storage, a modification of the normal 'cell age/cell density' relationship was observed, as erythrocytes were affected by changes in cell volume in an age-dependent manner. This may stem from a different impact of storage on the imbalance of monovalent cations, Na(+) and K(+), in young and old erythrocytes, related to their different complement of cation transporters.

An attempt to predict daily erythrocyte lithium fluctuations

Erythrocyte lithium concentration, which is a better predictor of brain lithium levels than plasma lithium concentrations, possesses the disadvantage of precise hourly determination following the last intake. The variability in RBC lithium accumulation increases as the extracellular lithium concentration increases. This increase is also time dependent and it would be very useful if the pharmacokinetic rate constant were known. Unfortunately, low lithium levels do not allow measurements within confidence intervals. In this work, we tried to determine, in vitro, the kinetic rate constants in erythrocytes of healthy volunteers. Different high lithium loaded plasma-like media were used for an extrapolation procedure of constants allowing the determination of an erythrocyte load constant namely K0 = 0.0161 +/- 0.0005 h-1 at corresponding plasma lithium concentrations. The abnormalities of lithium transport determined by in vitro procedures would be very useful in understanding the etiology of affective illness. Lithium flux pre-controls corrected with this rate constant would be very helpful in enlarging laboratory time management.

Evidence for multiple genes determining sodium transport

Sodium transport comprises a set of interacting systems. Consequently, a defective sodium transport gene affects multiple sodium transport systems, and a sodium transport variable measured on a sample of individuals reflects genetic variation from a number of different genes, complicating the task of identifying the effect of a single gene. To test for genes which affect sodium transport, we first applied principal components analysis to 14 variables related to sodium transport, thereby defining uncorrelated sources of variation in the variables. The sample consisted of 1,218 members of 68 pedigrees ascertained through probands with early-onset stroke, hypertension, or coronary heart disease. Segregation analysis of the 14 principal components scores provided evidence for 8 genetic variants which alter sodium transport. One of the 8 variants is recessive, has homozygous genotype frequency estimated as 8.8% of the population, and increases sodium-lithium countertransport, the passive sodium leak, body mass index, and triglyceride; the genetic variant may coincide with an insulin resistance gene. A second of the 8 variants is also recessive, has homozygous genotype frequency estimated as 7.4% of the population, and increases intraerythrocytic sodium and the passive sodium leak while decreasing sodium pump number; the genetic variant may reduce pump number. Two of the 8 variants substantially increase sodium-lithium countertransport; frequency estimates for heterozygotes for the dominant variant and homozygotes for the recessive variant equal 1.8% and 3.1%, respectively. Another of the 8 variants is recessive, has homozygous genotype frequency estimated as 1.9%, and increases body mass index. Each of the 3 remaining variants is rare and expressed in less than 1% of the sample.

The membrane defect in hereditary stomatocytosis

Hereditary stomatocytosis and allied conditions represent a series of diseases in which abnormal movements of univalent cations across the plasma membrane play an important part in cellular disease. The primary problem lies not in the active transporters but in the basal permeability of the membrane, which is always increased, and the extent of the increase correlates with the cellular dysfunction. A number of structural abnormalities have been described in these membranes, but the most consistent and convincing is the deficiency of a hitherto uncharacterized integral membrane protein of molecular weight 31 kDa in the severe, 'overhydrated' form of the disease. The true function of this protein remains enigmatic, but its deficiency in this condition indicates that it may have a role in the regulation of cation transport.

Membrane properties of erythrocytes in subjects undergoing multiple blood donations with or without recombinant erythropoietin

To examine the characteristics of 'young' human red cells, we studied blood from seven healthy male volunteers who developed systemic reticulocytosis during a 3-week blood donation period. Each of these subjects donated a total of 6 units (450 ml/unit) of blood (2 units/week for 3 weeks) with subcutaneous recombinant erythropoietin (SC rEPO; 200 U/kg daily for 3 weeks). Two of these subjects were also studied with a similar protocol in the absence of rEPO (4.5 +/- 0.5 units donated). SC rEPO administration was associated with an increased K content of the erythrocyte and with the appearance of hypochromic cells, which were initially normocytic and then became normochromic and microcytic. Measurements of cation transport revealed that, with the exception of the Na-K-Cl cotransport, all the systems studied increased their activities following blood donations with or without SC rEPO. The increase was highest in the K-Cl cotransport (2- and 5-fold for control and rEPO parts of the study, respectively), while the Na-K pump increased slightly in control and 40% with rEPO. The Na-Li countertransport increased 40% and 100% in the control and rEPO parts of the study, respectively. Concomitant with increased ion transport activity, electron microscopic studies of plasma and red cells of subjects receiving SC rEPO showed the presence of circulating exosomes and cytoplasmic multivesicular bodies. The transferrin receptor was detected in the circulating exosomes, thereby providing evidence that, as do nonhuman red cells, maturing human reticulocytes shed exosome-associated transferrin receptors.

Erythrocytic ouabain-sensitive sodium efflux rate constant in pregnancy

To elucidate the physiology of active sodium transport (expressed as erythrocytic ouabian-sensitive sodium efflux rate constant = ERCos) in pregnancy and the influence of dietary sodium intake on that transport, active sodium transport was measured in 52 healthy pregnant women in week 16, 20, 24, 28, 32, 36 or week 38 of gestation. ERCos was not influenced by parity, dietary sodium intake or the development of pregnancy-induced hypertension. A statistical significant shift in ERCos was detected between week 24 and week 28 of gestation accompanied by a shift in intracellular sodium content. The meaning of this change in pregnancy remains unsolved, but an influence of ANP through A-II is suggested.

Erythrocyte sodium, potassium and sodium fluxes with cell and subject ageing

In young subjects erythrocyte sodium was lower in females than in males. In males juvenile erythrocyte sodium decreased with subject age whereas in females aged erythrocyte sodium increased with subject age. Therefore, the difference in erythrocyte sodium between young male and female subjects was not observed in the elderly. These differences in erythrocyte sodium appeared to be mainly due to differences in the sodium pump rate constant. In juvenile cells from young subjects the sodium pump rate constant was related to the ouabain sensitive sodium flux rate, but not in elderly subjects, suggesting disturbed control of cell sodium in the latter group. Juvenile erythrocytes had a higher potassium content in elderly than young subjects but this was mainly in the 'frail' hospitalised elderly and it decreased more rapidly with cell ageing. This could indicate more active erythrocytes entering the blood in elderly subjects and then ageing more rapidly. Differences between young and elderly subjects in erythrocyte sodium, potassium and sodium pump rate constant were more marked in the 'frail' hospitalised elderly.

Diurnal variation of erythrocyte sodium-lithium countertransport rate and intracellular cation concentrations

Differences in erythrocyte sodium-lithium countertransport rate and erythrocyte potassium concentration were found between 0900 h and 2100 h in ten healthy individuals. Sodium-lithium countertransport rates were lowest at 0900 h (x: 0.34 mmol/l per h; SD: 0.15) and highest at 1200 h (x: 0.42 mmol/l per h; SD: 0.16). Erythrocyte potassium concentrations increased progressively during the day, while erythrocyte sodium concentrations did not change significantly during the day. For comparative and epidemiological studies of erythrocyte sodium-lithium countertransport rate blood samples should be taken at the same time of the day.

Erythrocyte rheology

Two main subjects of erythrocyte rheology, deformation and aggregation, are discussed in detail, on the basis of biochemical structure. The close relationship between the life span (or cell aging) and the rheology of individual erythrocytes is also briefly described. A currently important problem is emphasized, that is, the molecular aspect of the dynamic cytoskeletal structure and the mechanism of its regulation. This concerns not only the rheological function and the survival of circulating erythrocytes, but also the pathophysiology of abnormal erythrocytes.

Recessive inheritance of a high number of sodium pump sites

The number of sodium pump sites on erythrocytes was measured on 1,847 individuals in 80 Utah kindreds ascertained through probands with cardiovascular disease. Likelihood analysis supported recessive inheritance of high pump number. The major locus explained 14.0% of the variance in pump number; polygenic inheritance explained another 63.4%. Homozygotes for the recessive allele occurred with a frequency of 1.74% and had a mean pump number estimated as 566.0 sites/red blood cell (RBC) versus a mean of 312.2 sites/RBC for the other genotypes. Young individuals with the high pump number genotype were leaner, and older adults with the high pump number genotype were heavier. Diabetes and early hypertension were more prevalent in women with the high pump number genotype. Although not significant, obesity in adults of both sexes and early coronary heart disease in men were more prevalent in individuals with the high pump number genotype.

Sodium-lithium countertransport activity and its sensitivity to inhibitors with erythrocyte ageing in man

Sodium-lithium countertransport is believed to depend on a specific protein and since such proteins usually decline with erythrocyte age it would be expected to be reduced in older cells. In fact, sodium-lithium countertransport increased with ageing, whereas the rate constant of the sodium pump decreased. The increase in sodium-lithium countertransport with erythrocyte ageing was due to a phloretin insensitive component that was not present in young erythrocytes. Raised sodium-lithium countertransport in patients with essential hypertension was due mainly to an increased phloretin sensitive component but the phloretin insensitive component was also higher in middle aged erythrocytes. Amiloride had no effect upon sodium-lithium countertransport or unidirectional sodium influx in cells of any age. This suggests that sodium-lithium countertransport is not a mode of action of the sodium-proton exchanger in the erythrocyte.

A digoxin-like factor associates with erythrocyte sodium concentration, sodium transport, and ouabain binding

To investigate what effects a circulating digoxin-like factor (DLF) might have on sodium metabolism, we examined data collected on 1,327 individuals screened in the Cardiovascular Genetics Clinic at the University of Utah. This sample included 639 unmedicated adults, 582 youths under age 18, and 106 medicated hypertensive individuals, all on an unrestricted diet when attending clinic. No individuals look digitalis. A digoxin assay detected measurable levels of plasma DLF in 13.4% of the youths, 17.2% of the normotensive adults, and 25.5% of the hypertensive adults. In all three groups of individuals, those with a measurable DLF had a significantly lower erythrocyte ouabain sensitive sodium efflux rate constant (adjusted for age, sex and body mass) than those with no measurable DLF (p less than 0.01). Normotensive and hypertensive adults with measurable DLF also had an increased erythrocyte intracellular sodium level. Either the number of ouabain binding sites and/or the apparent affinity for ouabain were reduced for those with DLF levels in all three groups. There was a small nonsignificant increase in blood pressure for the normotensive adults and youths with a measurable DLF. We conclude that plasma DLF is associated with reduced ouabain sensitive sodium transport and increased intracellular sodium concentration, possibly due to changes in the number of or the competition for the Na+ - K+ ATPase sites.

The inheritance of intraerythrocytic sodium level

Intraerythrocytic sodium level (RBC Na) was measured on 1,800 normotensive members of 64 Utah pedigrees ascertained through hypertensive or normotensive probands, sibs with early stroke death, or brothers with early coronary disease. Likelihood analysis provided evidence that RBC Na was determined by four alleles at a single locus. Each allele was recessive to all alleles associated with a lower mean level. The four resultant distributions occurred in the frequencies: 0.8%, 89.3%, 9.7%, and 0.2% with corresponding means (mmol/1 RBC) of 4.32, 6.67, 9.06, and 12.19, respectively. The major locus explained 29.0% of the variance in RBC Na; polygenic inheritance explained another 54.6%. A higher frequency of the genotypes for high RBC Na in pedigrees when the proband was hypertensive than normotensive provided evidence that this major locus increases susceptibility to hypertension.

Familial correlations from genes and shared environment for urine, plasma, and intraerythrocytic sodium

Spouse-spouse, sib-sib, and parent-offspring correlations were calculated for urinary, plasma, and intracellular sodium levels on over 1,900 persons aged 3-86 years in 98 Utah kindreds. For 36 hours prior to their clinic visit, 31% of the sample was salt-loaded with salt tablets, while the rest followed their normal diet. For those on their normal diet, urine creatine-, age-, and sex-adjusted urinary sodium excretion from a timed 12-hour overnight sample showed similar and significant correlations between spouses (r = .29), sibs less than 20 years old (r = .38), and parent-offspring pairs for offspring less than 20 years old (r = .29). This contrasted with the lower correlations between sibs 20 years of age and older (r = .10) and parent-offspring pairs for offspring 20 years of age and older (r = .13), presumed to live in different households. Adult plasma sodium sib-sib (r = .13) and parent-offspring (r = .15) correlations were similar to the urinary sodium correlations, while the spouse-spouse (r = .48), the sib-sib (r = .64), and the parent-offspring (r = .63) correlations for those presumed to live in the same household nearly doubled. Intracellular sodium correlations for the adult sibs (r = .32) and offspring (r = .36) were over twice as large as for urinary or plasma sodium, although the spouse-spouse correlation (r = .37) remained large also.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary evidence for genetic determination of intraerythrocytic sodium concentration in Utah pedigrees

Intraerythrocytic sodium concentration has been reported to be increased in hypertensive individuals and some of their normotensive relatives. We investigated the "familiality" of this trait in 572 nonhypertensive subjects from 34 Utah kindreds. Most of these kindreds were selected because of a high incidence of hypertension, heart attack, or stroke. Intraerythrocytic sodium concentration was correlated with the sex of the subject and suprailiac skinfold thickness. Intraerythrocytic sodium concentration was adjusted by linear regression for these 2 factors. The residual values were positively correlated in parent-offspring pairs and among sibs, both those presumed to be living together and those presumed to be living apart. The spouse-spouse correlation was not significant. Pedigree analysis suggested a mixed major-gene/polygenic model of inheritance, but these data did not allow us to distinguish between dominant and recessive inheritance for the major gene component. Total heritability due to both major-gene and polygenic components was estimated to be 90-95%; the proportion of the total variance due to polygenes was estimated to be 60-75%. These results suggest that further study of the relationship between the inheritance of intraerythrocytic sodium and the pathophysiology of hypertension is warranted.